Characterization of VOC Emissions Using Mobile Laboratories

Characterization of VOC Emissions Using Mobile Laboratories

Image Credit: TOFWERK

The Vocus Elf PTR-TOF is made ideal for real-time mobile monitoring of VOCs by its rugged design and small footprint.

Characterization of VOC Emissions Using Mobile Laboratories

Researchers and regulatory authorities are able to map chemical emissions and chemical dispersal within environments with mobile laboratories equipped with fast, sensitive instrumentation. Along with direct mapping, mobile laboratories are able to locate and “fingerprint” point sources, understand ambient concentrations, and determine the real-world lifecycle of VOC emissions. This information provides crucial input for air quality modeling, environmental policy, and studies into public health.

Proton-transfer-reaction mass spectrometry (PTR-MS) is well established in its use in mobile lab applications because it allows the direct measurement of ambient air, and is able to distinguish individual VOCs in a complex sample matrix. Dozens of studies have benefitted from mobile laboratories equipped with conventional quadrupole PTR-MS (PTR-qMS), and measurements conducted with these instruments make up the foundation of modern atmospheric science.

Vocus Elf PTR-TOF offers the advantages of Vocus PTR time-of-flight mass spectrometry (multiple-Hz measurement speed, simultaneous measurement of all masses, and high sensitivity from the Vocus PTR reactor) at the size, price-point, and power requirements of PTR-qMS.

Feature Image: A Vocus Elf PTR-TOF mounted in an electric car was driven through the streets of Thun, Switzerland. The color and height of the markers shown along the drive path indicate the measured ambient concentration of toluene (C7H9+) at a 4-Hz measurement speed. 

Methods

For this study, a Vocus Elf was installed in the rear passenger seat of an electric car with a ratchet strap (Figure 1). It was not necessary to make special engineering modifications to the car. A 1/4” PFA line was run through the roof window of the car, which was used to sample the external air after it was attached to a longitudinal sampling probe that extended over the hood of the car. There was the risk of the instrument sampling the car’s own emissions. This risk was eliminated by driving the full 90 minute experiment time on full electric power and powering the Vocus Elf powered with the car battery.

Characterization of VOC Emissions Using Mobile Laboratories

Figure 1. Vocus Elf PTR-TOF installed in a vehicle. A PFA sampling tube attached to a longitudinal roof sampling probe (visible in the upper right corner of the image) was connected to the instrument inlet and small external pump. Image Credit: TOFWERK 

This particular drive path was chosen to include a number of major arterial streets, as well as the official air quality monitoring station, and other point sources such as gas stations, a water treatment plant, and the train station.

Spatial Characterization of VOC Emissions

Several VOC hotspots were immediately made visible to the operators during the drive. An overlay of the measured toluene on a map shows hotspots near the following areas:

  • Intersections
  • The train station
  • Arterial roads
  • Gas stations

It was found that there was sometimes an ambient concentration of over 100 ppbv in these areas (as shown in the feature image). Extremely high concentrations of BTX were detected near a large construction site on a major roadway, illustrated in Figure 2. Typically, single stationary monitoring stations are not sufficient to detect large, transient emission sources like these.

On over 100 unit-mass-integrated ions, enhanced signal was observed, and correlations between different compounds can be used to define the chemical “fingerprints”, or VOC profile composition, of different sources. A range of distinct sources were observed, including two potential, different combustion traffic-related sources, a source rich in toluene, another source rich in acetone, and a source containing especially m/Q 73, 91, 101, and 119. A distinct profile of aromatics makes combustion sources recognizable. It was hypothesized that the toluene source could possibly have been associated with the construction site. Additionally, the VOC detected at m/Q 101 was thought to possibly be hexanal or pentanedione from a nearby medical clinic.

Characterization of VOC Emissions Using Mobile Laboratories

Figure 2. High concentrations of BTX observed near a construction site along the Allmendstrasse. A time series of mixing ratios is shown in the upper panel, and the location of the hotspot is shown in the map in the bottom panel. Image Credit: TOFWERK 

Characterization of VOC Emissions Using Mobile Laboratories

Figure 3. Distinct sources detected in Thun. The map shows the drive track of the mobile laboratory through the city, with color and intensity indicating the identity and relative abundance of each source. The smaller panels show the mass spectral VOC fingerprint of each source. Image Credit: TOFWERK 

Acknowledgments

Produced from materials originally authored by Abigail Koss, Luca Cappellin, Christoph Gasser from TOFWERK.

This information has been sourced, reviewed and adapted from materials provided by TOFWERK.

For more information on this source, please visit TOFWERK.

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